Lubricating oil composition



Patented Aug. 24, 1954 UNITED STATES PATENT OFFICE LUBRICATING OILCOMPOSITION No Drawing. Application December 11, 1951, Serial No.261,142

7 Claims.

have hitherto been proposed as synthetic lubricants. These materials areprepared from the alkylene oxides, such as ethylene oxide, 1,2-propylene oxide, the 1,2-butylene oxides and higher homologs andmixtures thereof, and the corresponding alkylene glycols. The resultingproducts may be polyoxyalkylene diols or polyalkylene glycol derivativesin which one or both of the terminal hydroxyl groups have been removedeither during the polymerization reaction or subsequently thereto, as byetherification or esterification, to yield monoor di-ether or monoordi-ester groups, or combinations of such terminal groups, wherebycertain desirable properties are imparted to the final polymericmixture.

By way of illustration, U. S. Patent N 0. 2,448,664 describes thepreparation of a polyoxypropylene polymeric mixture according to theequation:

- R.(O CzHaCHshOH Polyoxypropylene monohyclroxy compound ROHn(OC2Ha.CH3)

Monohydric 1,2-propylene alcohol oxide Other patents coverpolyoxypropylene derivative of the foregoing monohydroxy compound inwhich the terminal hydroxyl group has been etherified or esterified.These materials are alleged to be useful as synthetic lubricants.

Although polymeric compounds prepared from the above-mentioned epoxidesand glycols have certain desirable properties, such as good viscosityindices, they possess the serious drawback of being highly sensitive tooxidation. Upon oxidation these polymeric materials depolymerize, withconsequent loss in viscosity, to form undesirable acidic compounds andvolatile materials, which latter materials are eventually lost from thelubrication system.

An object of the invention is to impart oxidative stability to polymericmixtures prepared from alkylene oxides or glycols.

Another object of the invention is to prepare novel and superiorlubricating oil compositions.

Other objects and advantages of the invention 2 will be apparent fromthe ensuing description of the invention.

The invention is predicated on the discovery that polymeric material ofthe type hereinabove described can substantially be made more resistantagainst oxidation by the incorporation therein of a polyhydroxy aromaticprimary inhibiting compound, for example, a dihydric phenol, and as asecondary inhibiting compound or activator for said primary inhibitingpolyhydroxy aromatic compound an aliphatic amine of the type hereinbelowdefined. The results are unexpected in view of the fact that thesecondary inhibitor or activator by itself has no anti-oxidant effect onpolyalkylene glycol polymeric material, but when used conjointly withthe primary inhibitor greatly enhances or activates the anti-oxidantproperties of the primary inhibitor.

More specifically, the primary inhibiting compound is a hydroxy aromaticcompound in which at least two hydroxyl groups appear on one ring, forexample hydroquinone, or on one aromatic nucleus, for example,l,2-dihydroxy-naphthalene. Classes of these compound are polyhydricphenols, naphthols, anthrols and the like, having a minimum solubilityin the polyalkylene glycol polymeric material of 0.25 per cent by weightof the polymeric material and preferably 0.5 per cent. The specificclass preferred is a dihydric phenol. Moreover, the polyhydroxy compoundcan have substituent groups on the aromatic ring or nucleus, such asamino, mercapto, alkoxy, aryloxy, thio, alkyl, aryl, alkaryl, andarylalkyl radicals, so long as there remain at least two free hydroxylgroups on at least one aromatic ring or nucleus, as aforesaid. However,substituent groups containing oxygen which are acidic or acidstrengthening in nature, such as nitro, sulfonic acid, and carboxylradicals, which are not further oxidizable are less desirable and forpractical purposes are avoided.

Example of primary inhibiting polyhydroxy aromatic compounds arehydroquinone, t-butyl hydroquinone, di-t-bu-tyl resorcinol,t-butylcatechol, 1,2-dihydroxy naphthalene, lA-dihydroxynaphthalene,1,2-dihydroxyl-phenyl benzene, 5 octyl-1,4-dihydroxynaphthalene,LB-dihydroxy- 5-cetoxybenzene, 1,2-dihydroxythianthrene, 1,2- dihydroxy4 aminonaphthalene and 1,2-dihydroxyi-isooctylamino benzene.

The secondary inhibiting amine compound, or activator for the primaryinhibitor, is an aliphatic amine and can be regarded as the condensationproduct or products of an a-hydroxyalkylamine, for example, ethanolamineor isopropanolamine,

and/or an alkylene diamine, for example, ethylene diamine or1,2-propylene diamine. The condensation product or products can be ofstraight, cyclic or branched-chain structure. Preferably employed inaccordance with the invention is a secondary inhibiting aminecondensation product having at least one free amino hydrogen or hydroxylradical in the molecule. Substituent groups, such as alkyl, aryl,alkaryl and arylalkyl radicals on the nitrogen are therefore notpreeluded, although as hereinabove indicated it is preferred to have atleast one free amino hydrogen or free hydroxyl radical in the molecule.

The condensation products contemplated by the invention may beillustrated by the following equations:

The secondary inhibiting amine compound is preferably one having amolecular weight of at least 125 and which is soluble in thepolyalkylene glycol polymeric material to the extent of at least 0.25%,preferably at least 0.5%, by weight of said polymeric materials.Examples of suitable secondary inhibiting amines are tetraethylenepentamine, polyethylene diamine (average molecular weight 1400),aminoethylmorpholine, triethanolamine, triethanolamine tristearate, N ,Ndioleoyl tetraethylenepentamine, hydroxyethyldiethylene triamine, N,N-di(aminoethyl) aniline, N phenyl diethanolamine, N ,N-di(2-ethylhexyl) tetraethylene pentamine, triisopropanolamine, anddipropylenetriamine.

In general, the amount of primary inhibiting polyhydroxy aromaticcompound required for the substantial inhibition of oxidativedeterioration of polyalkylene glycol polymeric material ranges fromabout 0.1% to 5% by weight of the finished oil, with a working range ofabout 0.2% to 2% 4 and an optimum of 1.0% by weight of the finished oil.The useful amount of secondary inhibiting amine, or activator, resideswithin the range of about 0.5% to 10 and most advantageously from 1% to3%, generally about 2%, by Weight of the finished oil.

The polymeric materials contemplated by the present invention may beprepared according to conventional methods. For example, U. S. PatentNo. 2,448,664 describes the preparation of polyoxypropylene monohydroxycompounds by the addition of 1,2-propylene oxide to a monohydroxyaliphatic alcohol to produce a polymeric mixture of lubricating oilviscosity ranging in molecular weight from around 500 up to 2,000 andhigher. The preparation of copolymeric polyalkylene oxide mixtures fromethylene oxide and propylene oxide are described in U. S. Patent No.2,425,755. Polyoxyalkylene diols are described in U. S. Patent No.2,480,185, While diethers of polyoxyalkylene diol are taught in U. S.Patent No. 2,520,614. Preferably employed in accordance with theinvention is the diether of polyalkylene glycol or the monoether ofpolyalkylene glycol ester, derived most advantageously from1,2-propylene oxide.

A convenient method of measuring the resistance to oxidation possessedby the compositions prepared in accordance with the invention is the useof the apparatus and procedure described in Industrial and EngineeringChemistry, vol. 28, page 26 (1936), wherein the rate of oxygen absorbedat constant pressure by a definite weight of oil is regarded as ameasure of the oxidative stability of the oil. According to thisprocedure, the oil sample is placed in an absorption cell, provided inthe bottom with a fine fritted-glass filter to disperse the oxygenstream, circulating through the system at a constant rate, into finebubbles. In obtaining the data hereinbelow appearing, the followingmodified apparatus and procedure were employed:

The oxidation or absorption cell i constructed of a large glass tubewith the head portion having a connection for introducing oxygen, anannular space surrounding the upper end of the tube and a fitting for aremovable high speed glass stirrer. The annular space contains potassiumhydroxide pellets for the removal of water, carbon dioxide, volatilealdehydes, etc. The lower portion of the cell which contains the testedsample is immersed in an oil bath at a temperature of about 340 F.During the test, the oil sample is rapidly agitated by means of a highspeed stirrer and is kept under a pressure of about 1 atmosphere of pureoxygen, the volume of oxygen added being automatically recorded. Thetime in hours required for grams of oil to absorb 1200 cc. of oxygen iscalled the induction period (I. P.) and represents the point at whichthe sample begins to absorb oxygen or oxidize.

The following tabulated data were obtained from a number of experimentsperformed in accordance with the test above described.

In Table I a number of secondary inhibiting amine compounds areexemplified in combination with the primary inhibiting polyhydroxyaromatic compound t- -butyl catechol, employed in an amount of 1.0%.Where otherwise not indicated by amounts appearing after the designatedsecondary inhibiting amine compound, the secondary inhibiting aminecompound or activator was used in amounts of 1%. In all instances thepolyalkylene glycol polymeric material was one prepared from1,2-propylene oxide and 2-ethylhexanol, the said polymeric materialhaving a molecular weight of about 1000. The degree of oxidativestability of each combination appears as the induction period (I. P.) inhours at 340 F.

TABLE I Eflect of polyhydrozry aromatic primary inhibitor 1 withinhibitor activators Activator (1% in Polypropylene Glycol 2-ethy1hexylmonoether, M. W. about 1,000)

With 1.0% t-butyl catecliol (I. P.,

l a-M w PM? woomou ow w mono!) Flurther illustrative of the invention,polypropylene diol polymeric material was prepared employing1,2-propylene oxide and water to initiate the polymerization reaction,the polymeric material having a molecular weight of about 600. Additionof 1.0% t-butyl catechol resulted in a composition having an inductionperiod of only 2.0 hours. Addition of both 1.0% t-butyl catechol and 1%of aminoethylmorpholine toanother portion of the same polymeric materialresulted in a composition having an induction period of 4.8 hours.

As a further example of the invention, a copolymer of ethylene oxide and1,2-propylene oxide was prepared employing 25 mol per cent ethyleneoxide and 7 5 mol per cent 1,2-propylene oxide, and z-ethylhexanol asthe reaction initiator, the final polymer having a molecular weight ofabout 800. Addition of 1.0% t-butyl catechol and 1% ofaminoethylmorpholine to this polymer resulted in a composition having aninduction period of 6.4 hours. Omission of aminoethylmorpholine resultedin a composition having an induction period of only 2.3 hours.

Another example of the invention is as follows: A sec.-butyl methylpolypropylene glycol diether having a molecular weight of about 600 wastreated with 1.0% t-butyl catechol and 1% aminoethylmorpholine. Theinduction period of the final composition was 3.0 hours. In the absenceof aminoethylmorpholine, the induction period was only one hour.

Still another example of the invention is as follows: A trimethyleneglycol polymer having a molecular weight of about 800 was treated with1.0% t-butyl catechol and 1% aminoethylmorpholine. The final compositionhad an induction period of 16.7 hours as compared with an inductionperiod of 9.1 hours when the aminoethylmorpholine is omitted from thecomposition.

In all cases, the use of the activating material alone, in the absenceof t-butyl catechol, gave no inhibition.

In Table II there are tabulated the data. obtained from combinations ofdifferent primary inhibiting compounds with the activatoraminoethylmorpholine. The polymeric material was the same as thatemployed in Table I, and the numerals have the same significance as inTable I.

6 TABLE 11 Efiect of inhibitor activator with poll/hydroxy aromaticprimary inhibitors (I. P., Hrs. at 340 F.)

Polyh ydroxy Aromatic Inhibitor 1% in Polypropylene Glycol 2-ethyl HexylWith 1% Monoether (M. W. about 1,000) 1 Amino- Without ethylmor-Activator pholine t-Butyl catechol .3 4. 4 l. 8 Di-t-butyl resorcinoL.2. 1 0. .2 Hydro quinone 6. 5 4. 0 1,2-Dihydroxynaphthalen 4. 5 .2. 41,4-Dihydroxynapl1thalene 6. 8 3. 5 1,2-Dihydroxy-i-isooctylaminobenzene 5. 1 2. 6 -naphfhnl 2, 1 2, 6Pentadecylphenol (2%) 0. 0 0. 1 2, fi-Di-t-butyl-p-cresol. 0. 2 0. 4m-Oetoxyphenol 0. 0 0. 0

It will be noted from inspection of the above table that phenolicprimary inhibitors which fall outside the class defined herein are notimproved by the use of the activating material. These are suchmonohydric phenolic materials as p thol, pentadecyl phenol,2,6-di-t-butyl-p-cresol, and m-cetoxyphenol.

Compositions prepared in accordance with the invention are useful ascrankcase lubricants, hydraulic fluids, turbine oils, instrument oils,ice machine oils, constituent oils in grease manufacture, etc.

Obviously many modifications and variations of the invention, ashereinbefore set forth, may be made without departing from the spiritand scope thereof, and therefore only such limitations should be imposedas are indicated in the appended claims.

We claim:

1. A lubricant composition comprising a major portion of polyalkyleneglycol polymeric material of lubricating oil viscosity which issusceptible to oxidative deterioration, together with from 0.1 to 5% byweight of a hydroxy aromatic compound having two hydroxyl groups on anaromatic nucleus and from 0.5 to 10% by weight of an aliphatic amineselected from the group consisting of tetraethylenepentamine,triisopropanolamine, polyethylene diamine, aminoethylmorpholine,triethanolamine, dipropylenetriamine, aminoethylethanolamine,hydroxyethlydiethylenetriamine, N ,N dioleoyltetraethylenepentamine, andtriethanolamine tristearate, said hydroxy aromatic compound and saidaliphatic amine each being soluble in said polyalkylene glycol polymericmaterial to the extent of at least 0.25 by Weight.

2. The composition of claim 1 wherein the polyalkylene glycol polymericmaterial is a 1,2- polyalkylene glycol polymer wherein at least one ofthe end groups is an alkoxy group.

3. The composition of claim 2 wherein the hydroxy aromatic compound istertiarybutylcatech01.

4. The composition of claim 2 wherein the polyalkylene glycol is apoly-1,2-propylene glycol monoalkyl ether, the hydroxy aromatic compoundis tertiarybutylcatechol and the aliphatic amine isaminoethylmorpholine.

5. The composition of claim 2 wherein the polyalkylene glycol is apoly-1,2-propylene glycol monoalkyl ether, the hydroxy aromatic compoundis tertiarybutylcatechol and the aliphatic amine is triethanolamine.

6. The composition of claim 2 wherein the polyalkylene glycol is apoly-1,2-propylene glycol 7 monoalkyl ether, the hydroxy aromaticcompound is tertiarybutylcatechol and the aliphatic amine istetraethylenepentamine.

7. The composition of claim 2 wherein the polyalkylene glycol is apoly-1,2-propy1ene glycol monoalkyl ether, the hydroxy aromatic compound is tertiarybutylcatechol and the aliphatic amine istriisopropanolamine.

References Cited in the file of this patent UNITED STATES PATENTS NumberNumber Name Date Ballard et a1 Sept. 6, 1949 Ballard et a1 Sept. 12,1950 FOREIGN PATENTS Country Date Great Britain Mar. 20, 1935 GreatBritain May 5, 1948

1. A LUBRICANT COMPOSITION COMPRISING A MAJOR PORTION OF POLYALKLENEGLYCOL POLYMERIC MATERIAL OR LUBRICATING OIL VISCOSITY WHICH ISSUSCEPTIBLE TO OXIDATIVE DETERIORATION, TOGETHER WITH FROM 0.1 TO 5% BYWEIGHT OF A HYDROXY AROMATIC COMPOUND HAVING TWO HYDROXYL GROUPS ON ANAROMATIC NUCLEUS AND FROM 0.5 TO 10% BY WEIGHT OF AN ALIPHATIC AMINESELECTED FROM THE GROUP CONSISTING OF TETRAETHYLENEPENTAMINE,TRIISOPROPANOLAMINE, POLYETHYLENE DIAMINE, AMINETHYMORPHOLINE,TRETHANOLAMINE, DIPROPYLENETRIAMINE, AMINOETHYLETHANOLAMINE,HYDROXYETHLYDIETHYLENTERIAMINE, N1,5 - DIOLEOYLTETRAETHYLENEPENTAMINE,AND TRIETHANOLAMINE TRISTEARATE, AND HYDROXY AROMATIC COMPOUND AND SAIDALIPHATIC AMINE EACH BEING SOLUBLE IN SAID POLYALKYLENE GLYCOL POLYMERICMATERIAL TO THE EXTENT OF AT LEAST O.25 BY WEIGHT.